1. Field of the Invention
This invention relates to hydrocarbon fluid compositions and their use in industrial applications in general.
2. Brief Description of Related Art
Fluids are widely used in many industries, especially in the petroleum industry where different fluids are used in different operations including drilling, completion, wellbore cleaning, stimulation, and pipeline cleaning operations. There are two general classes of fluids: water-based fluids and non-aqueous based fluids. Alcohol-based fluids and hydrocarbon-based fluids are generally classified as non-aqueous fluids.
In general, when fluids are used in subterranean operations, the nature of the subterranean formation to a large extent dictates which types of fluids are suitable for use in such operations. Due to their low cost and high versatility, water-based fluids are normally preferred. However, certain subterranean formations are susceptible to water. When exposed to water, hydrocarbon production may decrease in such formations because of clay swelling and migration. For such water-sensitive formations, hydrocarbon-based fluids are generally preferred.
For drilling in water-sensitive formations, invert emulsion muds (fluid compositions containing a certain amount of water emulsified in oil), are widely used. An emulsion can be defined as the dispersion of one liquid, called internal phase, in another liquid, called the external or continuous phase. In invert emulsion muds, water droplets are dispersed in oil. Normally invert emulsion muds can contain about 50% of water. The disadvantages of the invert emulsion muds are their high costs and the extensive preparation and quality control required.
Hydraulic fracturing has been used for decades to enhance petroleum production. In hydraulic fracturing operations, a fracturing fluid is injected through a wellbore into the formation at a pressure sufficient to overcome the overburden stress and thus initiate fractures in the formation. Following the initiation of the fractures, solid particles called proppants, are mixed in the fracturing fluid and transported into the fractures. The function of proppants is to prevent the fractures from closing back when the pressure is released. There are different proppants including sands, ceramics, resin-coated sands and the like. The most common proppants are sands. The proppant-filled fractures provide highly permeable channels allowing petroleum to seep efficiently through the fractures into the wellbore.
Water-based fracturing fluids are by far the most commonly used. For water-sensitive formations, however, hydrocarbon-base fracturing fluids are generally preferred. To improve solid-carrying capability, hydrocarbon fluids are often gelled by adding gelling agents. There are two major types of gelling agents: alkyl phosphate esters crosslinked by aluminum or iron salts, and aluminum fatty acid salts including aluminum octoate and aluminum stearate.
In the oil field operations, especially in fracturing operations, alkyl phosphate esters crosslinked by aluminum or iron salts are widely used. To prepare the fluid a phosphate ester and an aluminum or iron salts are mixed into a hydrocarbon liquid. The in situ reaction between the phosphate ester and the aluminum or iron salt form aluminum or iron phosphate esters which further form three-dimensional networks gelling the hydrocarbon fluid. This method is well known in the art and examples can be found in U.S. Pat. Nos. 3,505,374; 3,990,978; 4,003,393; 4,316,810; 5,110,485; 5,693,837 and 6,297,210.
Recently, however, it has been found that excess amounts of phosphorus residues in crude oil causes fouling problems in refinery towers. To clean out the fouling, refinery towers have to be prematurely shut-down, at significant financial cost. It is believed that the excess amount of phosphorus residues in crude oil stems mainly from the phosphate esters used in the hydrocarbon-based fracturing fluids. Therefore, there is a general demand for fracturing and other well operations to use hydrocarbon-based fluids which contain no phosphate esters while at the same time have good solid carrying capability and low fluid loss.
An alternative is to use aluminum soaps, which contain no phosphorous, to gel the hydrocarbon fluids for oil field operations, in particular for fracturing operations. Aluminum soaps have been used to gel hydrocarbon fluids in many applications, especially in ink industry.
Unfortunately, compared to aluminum or ferric phosphate ester, hydrocarbon fluids gelled by the aluminum soaps such as aluminum octoate is in general less viscoelastic, or in order to achieve comparable viscoelastic property more aluminum octoate is required, which increases the cost. Good viscoelasticity is important for carrying solid particles such as proppants.